Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$72.99	11.736%	$81.5561	$81.56	$81.55	$81.60
Purchase #2	$221.80	5.397%	$233.7705	$233.77	$233.75	$233.80
Purchase #3	$71.80	8.671%	$78.0258	$78.03	$78.05	$78.00
Purchase #4	$86.36	9.175%	$94.2835	$94.28	$94.30	$94.30
Purchase #5	$222.71	13.552%	$252.8917	$252.89	$252.90	$252.90
Purchase #6	$15.83	4.488%	$16.5405	$16.54	$16.55	$16.50
Purchase #7	$75.94	3.533%	$78.623	$78.62	$78.60	$78.60
7 purchase totals =	$767.43		$835.6911	$835.69	$835.70	$835.70